EAGER: Chemical Design for Controlling Electronic Properties of Organic Semiconductors and Molecules via Edge-On Gating

Luping Yu, University of Chicago, DMR 1242729

In this project we have investigated the edge-on gating effect in a molecular wire system. By incorporating cyclophane as the gate of the molecular wire, we demonstrated that electrical properties such as conductance can be controlled. It was observed that the orbital energy level and charge carrier’s tunneling barriers can be tuned by changing the gating group from strong electron acceptors to strong electron donors. The single molecule conductance and current-voltage characteristics of this molecular system are truly similar to those expected for an actual single molecular transistor.

In addition, the effect of protonation of the cyclophane pyridine on the conductance of the molecular wire system was studied. It was found that protonation effectively reduce the conductance of the wires regardless of the gating group, reversibly. This switching behavior will be important for realizing a true molecular transistor.

Figure 1. Chemical Structure of the cyclophane molecular wires.

Figure 2. (a) A representative metal-molecule-metal junction in STM break-junction technique. (b) Sample conductance traces of mlecular junctions. (c) Conductance histogram of the five molecular junctions. (d) Single current-voltage characteristic curves of the five molecular junctions.

Figure 3. (a) A plot of conductance at 0.1 V (red) and 1.5 V (blue) against difference in charge of the pyridine N of the molecular wires. (b) A plot of conductance against Hammet parameters of the corresponding functional group attached at the gate position.

Figure 4. Protonation effect on the conductance of the molecular wires with different gating groups.

Educational outreach and diversity:This interdisciplinary project offers opportunity for training graudate and postdoctoral associate in organic synthesis, break junction STM (BJSTM) measurements, and theoretical calculation using density functional theory. Inspired by the success of the last year, we have succeeded in recruiting a female graduate student (Dongling Zhao) and a female postdoctoral associate (Dr. Aireal Jenkins) to our group. A new postdoctoral associate Pianwei Li was recruited to perform charge transport measurements using BJSTM. Most recently, we also recruited a female high school student (Miss Jessica Lu ) to join us for summer research. At the same time, our group is hosting an international REW student from Zhejiang University of China, who is engaged in synthesis of new molecular electronic component for preparing highly thermally stable molecular assemblies.

Outreach: The PI has succeeded in establishing more collaborations with several companies, including Solarmer Energy for solar cell devices, Zhejiang Pharmas. Solarmer just negothiated the sharing arrangement of our patents’ right with Phllipe 66 company. In the past three years, the PI enjoys close collaborations with several research groups and national and industrial labs: Prof. Tobin J. Marks at Northwest University on device fabrication and characterization; Dr. Lin Chen at Argonne National Lab (ANL) on electronic dynamics of low band gap polymers; Professor Yang Yang at UCLA on Inverted solar cells; Dr. Dean M. DeLongchamp (NIST), on OPV polymer morphologies, Professor R Izquierdo from Université du Québec à Montréal, Canada on environmental sensors using OPV detectors. All of these collaborations resulted in publications in highly respected journals. An important collaboration with Hong Kong University on organic electronic materials is undergoing.

EAGER: Chemical Design for Controlling Electronic Properties of Organic Semiconductors and Molecules via Edge-On Gating

Luping Yu, University of Chicago, DMR 1242729